/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.hama.graph;

import java.io.IOException;

import org.apache.hadoop.fs.FileSystem;

/**
 * <code>OutputFormat</code> describes the output-specification for a Angrapa
 * job.
 * 
 * <p>
 * The Angrapa framework relies on the <code>OutputFormat</code> of the job
 * to:
 * <p>
 * <ol>
 * <li> Validate the output-specification of the job. For e.g. check that the
 * output directory doesn't already exist.
 * <li> Provide the {@link RecordWriter} implementation to be used to write out
 * the output files of the job. Output files are stored in a {@link FileSystem}.
 * </li>
 * </ol>
 * 
 * @see RecordWriter
 */
public abstract class OutputFormat<K, V> {

  /**
   * Get the {@link RecordWriter} for the given task.
   * 
   * @param context the information about the current task.
   * @return a {@link RecordWriter} to write the output for the job.
   * @throws IOException
   */
  public abstract RecordWriter<K, V> getRecordWriter(TaskAttemptContext context)
      throws IOException, InterruptedException;

  /**
   * Check for validity of the output-specification for the job.
   * 
   * <p>
   * This is to validate the output specification for the job when it is a job
   * is submitted. Typically checks that it does not already exist, throwing an
   * exception when it already exists, so that output is not overwritten.
   * </p>
   * 
   * @param context information about the job
   * @throws IOException when output should not be attempted
   */
  public abstract void checkOutputSpecs(JobContext context) throws IOException,
      InterruptedException;

  /**
   * Get the output committer for this output format. This is responsible for
   * ensuring the output is committed correctly.
   * 
   * @param context the task context
   * @return an output committer
   * @throws IOException
   * @throws InterruptedException
   */
  public abstract OutputCommitter getOutputCommitter(TaskAttemptContext context)
      throws IOException, InterruptedException;
}
